Radial flow turbine wheel for a gas turbine engine

ABSTRACT

A radial-flow turbine wheel for a gas turbine engine includes a Scallop Radius defined between an axis of rotation and the backface between each of the plurality of turbine blades, a Tip Radius defined between the axis of rotation and a tip of each of the plurality of turbine blades such that a Scallop Radius/Tip Radius defines a ratio less than 0.6. This enables a lower temperature scallop region which drives lower transient stresses and increases the Low Cycle Fatigue life of the turbine wheel.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

This disclosure was made with Government support under N00019-06-C-0081 awarded by The United States Navy. The Government has certain rights in this disclosure.

BACKGROUND

The present disclosure relates to a gas turbine engine and more particularly to a turbine wheel for an auxiliary power unit (APU).

An APU is often utilized to supplement main propulsion engines to provide electrical and/or pneumatic power as well as start the main propulsion engines. An APU is typically a gas turbine engine that includes a compressor, combustor, and turbine. The APU radial turbine wheels experience high tensile and compressive stresses during start up and shutdown.

SUMMARY

A radial-flow turbine wheel for a gas turbine engine according to an exemplary aspect of the present disclosure includes a plurality of turbine blades formed around a hub at constant intervals to form a scallop at the backface, a Scallop Radius (SR) defined between the axis of rotation and the backface between each of the plurality of turbine blades, a Tip Radius (TR) defined between the axis of rotation and a tip of each of the plurality of turbine blades such that a Scallop Radius (SR)/Tip Radius (TR) defines a ratio less than 0.6.

BRIEF DESCRIPTION OF THE DRAWINGS

Various features will become apparent to those skilled in the art from the following detailed description of the disclosed non-limiting embodiment. The drawings that accompany the detailed description can be briefly described as follows:

FIG. 1 is a general perspective view of an exemplarily rotary-wing aircraft for use with one non-limiting embodiment of the present invention;

FIG. 2 is a partial phantom view of a rotary-wing aircraft illustrating a power plant system;

FIG. 3 is a general sectional view of an auxiliary power unit;

FIG. 4 is a general perspective rear view of a turbine wheel;

FIG. 5 is a general perspective front rear view of the turbine wheel; and

FIG. 6 is an expanded rear view of a scallop of the turbine wheel.

DETAILED DESCRIPTION

FIG. 1 schematically illustrates a rotary-wing aircraft 10 having a main rotor system 12. The aircraft 10 includes an airframe 14 having an extending tail 16 which mounts an anti-torque system 18. The main rotor system 12 is driven about an axis of rotation R through a main rotor gearbox (MGB) 20 (FIG. 2) by a multi-engine powerplant system 22—here having three engine packages ENG1, ENG2, ENG3 as well as an Auxiliary Power Unit (APU) 24 (FIG. 3). The multi-engine powerplant system 22 generates the power available for flight operations and couples such power to the main rotor assembly 12 through the MGB 20. Although a particular helicopter configuration is illustrated and described in the disclosed embodiment, other configurations and/or machines, such as high speed compound rotary-wing aircraft with supplemental translational thrust systems, dual contra-rotating, coaxial rotor system aircraft, turbo-props, tilt-rotor, fixed wing aircraft and non-aircraft applications such as ground vehicles will also benefit herefrom.

Referring to FIGS. 3-5, a turbine wheel 30T according to one non-limiting embodiment includes a hub 32 and a plurality of turbine blades 34 formed around the hub 32 at constant intervals.

The turbine wheel 30T is defined about an axis of rotation A. A shaft 36 extends from the turbine wheel 30T and through a compressor wheel 30C (FIG. 3) such that the turbine wheel 30T and compressor wheel 30C are coaxially coupled. The turbine blades 34 convert pressure energy of an exhaust gas from a combustor section 42 (FIG. 3) into rotational energy of the turbine wheel 30T. The turbine blades 34 are shaped such that high pressure combusted gas impinges on them while traveling down the gas path GF, causing shaft 36 to rotate (counter-clockwise in FIG. 4), thereby converting this heat and pressure into mechanical energy.

A scallop 38 is formed between the turbine blades 34 so that the backface 32P of the hub 32 is formed in an inwardly concave shape (also illustrated in FIG. 6). That is, the scallop 38 forms an inwardly concave shape within the backface 32P. The scallop 38 blends the rear edges 34RE of each adjacent pair of turbine blades 34 into the backface 32P of the hub 32.

The turbine wheel 30T experiences high compressive and tensile stress in the scallop 38 region during startup and shutdown. During startup, the turbine blades 34 warm up faster than the hub 32 which causes high compressive thermal stresses at the scallops 38. During shutdown, the turbine blades 34 cool down faster than the hub 32 which causes high tensile thermal stresses at the scallops 38. The magnitude of these transient thermal stresses depends of the temperature gradient between the scallops 38 and the axial center of the turbine wheel 30T. Since the temperature is highest at 34T and decreases radially through the part, lowering the Scallop Radius (SR) decreases the temperature at the scallops 38, which decreases the transient temperature delta they experience. This then decreases the transient stress, increasing the Low Cycle Fatigue (LCF) life of the turbine wheel 30T.

A Scallop Radius (SR) is defined between the axis of rotation A and diameter 32H of the hub 32 at the scallop between each pair of blades 34. (see FIG. 6). A Tip Radius (TR) is defined between the axis of rotation A and a tip 34T of each blade 34. In one non-limiting embodiment, the Scallop Radius (SR) is 2.08 inches (5.28 cm) and the Tip Radius (TR) is 3.81 inches (9.68 cm) such that the Scallop Radius (SR)/Tip Radius (TR) defines a ratio less than 0.6 and more specifically approximately 0.55, which is significantly smaller than conventional designs. The relatively low ratio alleviates the issue of compressive and tensile thermal stress during startup and shutdown by extending the scallop 38 deep into a region where the thermal gradient is less severe.

It should be understood that relative positional terms such as “forward,” “aft,” “upper,” “lower,” “above,” “below,” and the like are with reference to a normal operational attitude but should not be considered otherwise limiting.

It should be understood that like reference numerals identify corresponding or similar elements throughout the several drawings. It should also be understood that although a particular component arrangement is disclosed in the illustrated embodiment, other arrangements will benefit herefrom.

Although particular step sequences are shown, described, and claimed, it should be understood that steps may be performed in any order, separated or combined unless otherwise indicated and will still benefit from the present disclosure.

The foregoing description is exemplary rather than defined by the limitations within. Various non-limiting embodiments are disclosed herein, however, one of ordinary skill in the art would recognize that various modifications and variations in light of the above teachings will fall within the scope of the appended claims. It is therefore to be understood that within the scope of the appended claims, the disclosure may be practiced other than as specifically described. For that reason the appended claims should be studied to determine true scope and content. 

1. A radial-flow turbine wheel for a gas turbine engine comprising: a hub having a backface defined about an axis of rotation; and a plurality of turbine blades formed around said hub at constant intervals to form a scallop in said backface, a Scallop Radius defined between said axis of rotation and said backface between each of said plurality of turbine blades, a Tip Radius defined between said axis of rotation and a tip of each of said plurality of turbine blades such that a Scallop Radius/Tip Radius defines a ratio less than 0.6.
 2. The radial-flow turbine wheel as recited in claim 1, wherein said scallop forms an inwardly concave shape within said backface.
 3. The radial-flow turbine wheel as recited in claim 2, wherein said scallop blends a rear edge of each of said plurality of turbine blades.
 4. The radial-flow turbine wheel as recited in claim 1, wherein said plurality of turbine blades extend from said backface.
 5. The radial-flow turbine wheel as recited in claim 1, wherein said Scallop Radius/Tip Radius defines a ratio of 0.55. 